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Triumph TR6 - Rough Idle/popping on deceleration

Ok guys I am at the point where if I pull out any more hair I shall be bald! My 71 now is popping (misfiring) a lot at idle and also on deceleration (popping).
I started to muck-about with the air fuel mixture screw and that is when my problem started. I was attempting to use the colour tune to set the carbs up exactly but had no change in colour (bright yellow = to rich). My front carb spark plugs look a nice grey/brown colour. The back 3 are fouled black. With timing light it appears that the misfire is in the back three. Timing appears ok and is rock solid steady. I run pertronics EI. So with black plugs one would say u are running rich so I lean out the back carb (1/4 turn of the adjusting screw CCW). Now comes the interesting point. Lifting the piston with a screwdriver the engine stalls immediately! This says to lean! (The front carb does the rise in RPM then back...this is good!) It seems that no mater how much I turn the adjusting screw CW or CCW I still get the stall when lifting the piston with a screwdriver. I know I only have 3 full turns (CCW) from the full stop (CW) before the threads disengage between the adjusting screw and the needle itself. Also no matter where the needle is adjusted I still have misfire on idle. Engine sounds fine (no misfire) when at running speed. I have the vacuum retard hose to the back carb pluged at both ends. I have tightend the intake and exhaust mounting bolts. I have sprayed carb cleaner around the possible vacuum leak points. The carb mounting bolts are tight.
Maybe I am chasing a bunch of "red hearings" here as I am trying to keep in mind that this all started when I adjusted the needle valve and I have had that off a dozen times! The diaphram looks good.
So please offer up your suggestions to an older chap that does not wish to become any more balder.
Rick C
Rick Crawford

Do you enjoy beverages? You know what they say, 90% of the time it's ignition related. So (one at a time) replace your cap, rotor, and wires with the new spares you have tucked in the boot. I had similar problems (misfire off idle, but fine at speed) a couple of weeks ago and found the fuel pump to be weak. Replaced the pump and I was back on the road with a smile.
Rick Orthen

Hi Rick USA
Did you run any special test to determine a weak fuel pump ??? How can we tell?
Charlie
Charlie

Rick & Charlie
My local liquor/beer store ( that is how small a town I am in ..one store) has already this week had to do an emergency reorder of Black Label (beer).
So like Charlie says..how do we determine a week fuel pump? Rick O this happened literally over the course of 10 minutes as I adjusted the needle valve.
Now the interesting thing is that with the timing light clamped to #6 wire I get almost a solid on flash rather than a...well...you know what it should look like at idle. Rick O all the stuff on the spark plug side of the engine has only 1000 miles on it. Wire set is 8MM and plugs are only 400 miles old. I will take a closer look at the firing of the individual plugs. Thanks for the help so far guys.
Rick C
Rick Crawford

Charlie/Rick C.

Hmmm, didn't catch first that the "event" happened in a span of 10 minutes. I'd pull the top off the rear carb and make sure everything is in order (needle base flush with bottom of piston, diaphram OK). I've had new caps and rotors fail early, so don't bank on that being necessarily not the source. Like you suggested, time each wire for irregularities.

Regarding the weak fuel delivery, I was at my wits end and decided to replace the one component that hadn't been service recently--the fuel pump. Before pulling it, I disconnected the fuel line elbow at the front carb and had my son crank the engine to observe and visually benchmark the delivery. Very subjective mind you. Then I renewed the pump and cranked again. There was a noticeable improvement, and the misfire problem was gone. Caution: be prepared to replace the steel line from the pump to the carbs as the brass "olive" wouldn't seal again. The only fix was to cut the olive section out, use a new olive, and make up the length difference with fuel hose and clamps at the bend by the alternator.
Rick Orthen

Hi Rick Orthen

Is it possible your exhaust is plugged partially.My 72 dropped a bit of inside garbage and reacted the same way. Maybe the tune thing was just when it happened you know rev rev. Don't have an internal schematic of carb passages but maybe a bit of foul got loose when you were adjusting. Although your tester should not change when you adjust mixture. If your mixture looks ok at idle. and at say 2500 rpm it pretty much has to be exhaust. The odds of three plugs three wires or dist. are slim.

New to your sight guys have been playing with Trs for 20 years. TR 250 sadly gone 1 Tr6 15 mine working on total frame off. Welding in new frame parts at this time. Have all my hair and a big White beard to boot.

Bill Brayford
Guelph Ont.
B Brayford

I would think if fuel pump is low on presure it would effect all cyls.I say it is a bad carb. Someone once suggested to put the points back in and see if it clears up.
Don K.

DON KELLY

Charlie/Rick

Fuel pressure can be tested with a fuel pressure gauge quite accurately. It should stay steady without pulses in a range. I am at home and my Leyland manual is at my shop but I would imagine 4 to 6 lbs. normal. I do work on way more GM engines though so thats a guess I spend more time Hot Rodding than my old Brit. so if you don't have the spec. I will look it up for you.

Rick Crawford
Sorry about the mixup name in previous e-mail. Do you have an inline fuel filter check all filters. Damper oil top up. Crank walk can cause strange timing but should not affect back cylinders only. Will cause strange problems though on acceleration and deceleration. If you have a fuel pressure gauge mock up an offset line to the problem carb. and check against full line pressure. Check choke settings if front carb is on partial choke back carb off choke will cause problems. Not familiar with pertronics EI but watch for your light pulses as previously mentioned. The problem with some of them can be shorting between the capacitors your funny 6th or even poor grounding. Each device is different in its tech. I make my living servicing electronics particularily laser printers. 35 years ago I probably could have given you a schematic of what likely is the problem. Now unfortunately its replace the bitch. Fought with a Yamaha 650 EI for 2 years same symptoms my son just pointed out. Gave in spent $560 and works great. After carefull thought and a re-read see if you have a good quality spark at back cylinders as compared to front. If your EI has gone this will change at speed as different circuits are used. If the EI sets timing off at on the back plugs depending on circuitry you are going to have problems and fould plugs. My best bet is fuel starvation to carb. externally or internally on idle rich off idle lean

Have Fun but please let me know.

Bill Brayford

B Brayford

Rick C,
I've heard a couple of guys in the club say they
pulled their Pertronics out and went back to points.
I used a Pertronics "40,000 volt Flame Thrower" coil
in my old /66 Mustang and threw it out cause it was
only putting out 8,000 volts.
Good luck
Chris
Christopher Trace

Stromberg carbs? These are prone to rupturing the neoprene diaphragm, resulting in loss of piston lift as throttle is opened. Worth checking.
Peter cobbold

Hello to all
Thanks for the advise so far guys...I am getting balder and Bill, my beard is plenty grey.
Checked the firing of all six plugs with timing light and was a steady flash for each one...mind you this only tells you there is voltage to the plug. Have not gone back to points with last statement in mind. Swapped out the back 3 plugs with my Champion set and made no difference so went back to the Platinum set...still popping on idle. Reset all the valve clearances..no difference. Went a little richer as plugs where a little on the white side. Sprayed carb cleaner all over the place and no leaks. The diaphram is like brand new. I am idling around 900 RPM and about 16* BTDC. I have not checked fuel flow or have not done a compression test. There is good throttle response on " hammer down". Any other thoughts or suggestions much appreciated.
Rick C
P.S. does anyone know thr GAP between the magnet and pick up of the Pertronics EI? I have managed to loose the booklet and the plastic gapping tool.
Rick Crawford

I use two sheets of paper to set the Pertronix rotor gap. Works fine for me.
Rick Orthen

Hi Rick
Have you fully checked your brake servo vaccum line. I pulled my carbs and manifold out of the cupboard at shop and did a quick test. Only item I found short of the carb that affects mostly rear 3. Although it draws from all three intakes 2/3 is from rear three which of course it sits above. if you were leaning on it or setting tools while adjusting rear carb could be coincidence check all over both ends and especialy in the clamp on valve cover. I noticed mine has a split inside which would be leaking.

Luck
Bill
B Brayford

Rick,
Alright, You are bald enough.
Call Joe Dukovac at J.D. Auto service in Etobicoke
416 746 1048 Joe has a very sofisticated Sun Machine
diagnostic scope, more than half their work is British
but he has a terriffic diagnostic skill.
I know we would all like to figure out our own problems, but the nights are getting colder and soon
the days too. He'll figure it out within an hour
and you'll have the rest of the season.
see ya at Bronte
Christopher Trace

Bill and Chris
I removed and pluged the brake servo vaccumn line at the intake and no difference. Chris thanks for the info. I am (unfortunately) a stuborn TR6 owner and I will not let her win! So here is the latest.
I noticed while ballacing the carbs that even after adjusting the needles that the front carb was sucking a lot more air. I could hear it! I used Don Es. suggestion and used a length of heater hose ( did not want to cut up the garden hose:) and there was deffinitely a louder "roar" from the front carb. Keep in mind that the unisyn carb ballancer said they where ballanced. I did notice that the idle stop screw on the front carb was not even touching the stop and this is what got me to get out the hose. It was the end of the day and next morning went for a ride and could not get the idle below 2000 RPM. I back off both idle stop screws and still racing. You could hear and feal the more air being sucked into the front carb. So off comes the dash pot and everything looks AOK. Started her up and thought maybe the BP valve. Turned it and sure enough the idle drops to normal. I played with it a bit and you could start to hear more air being sucked in then the idle would increase drastically. I backed it off to bring the idle back down. So I started adjusting the back BPV and it made no difference at all in its position. I have had them off and the valve will move within its flexible material. I think I will just set the back carb one to same position as the front.
I still have the popping on idle...BUMMER!
Rick C
Rick Crawford

Hi Rick

I am assuming you have Stromberg Carbs. It would seem they played around with end of year etc. Do you have a vacuum port under back carb. Would be impossible to see with carbs in car feel under there just back of drain plug in bowel. A 71 orig. should not have this vac. port? maybe. If its there is it attached to water temp. valve. Check if its there. Again I don't know your engine. I am like yourself. I don't like to have machines beat me. Wife thinks I should know engine well. I have thought about it more than her for the last couple of days. Little cranky. Possible tune up due.


Because of the other fellow with problems is there a change at idle clutch in clutch out? Don't care about load. Let it settle down for a minute. Please let me know. Something I am trying to determine about crankwalk symptoms.

Thinking out loud

Everything you are telling me says vacuum leak or plugged internal ports for fuel in rear carb. I would look for float on throttle but not at idle anything should be ok short of the Bowel drain being out and gas on shoes should alert you to that. I did see something about Black Label beer though so maybe not. Try a few low test Coors and a nice single malt scotch to finish off, I find the combo gives you a much better nose for things. But your report of high air flow through front carb goes back to vac leak at rear? Or throttle disk choke closed. Maybe Equaliser in intake is actually feeding rear cylinders from front carb Common sense tells me. It has to be carb cannot pull fuel due to 1: Major Vac leak! resriction in fuel flow only in or to back carb? Throttle, choke disk back carb is closed. Why in 10 minutes throws me.

Lets try this.

If back carb throttle plate, choke out of sync. with front. Initial problem rich fouled plugs at back front plugs OK. PART CHOKE ON BACK CARB. FRONT OFF NORMAL. ADJUSTMENTS MADE MAY HAVE CLOSED BACK CARB? CHOKE/THROTTLE PLATE COMPLETELY. BACK CARB NOW OUT OF PICURE EXCEPT UNDER THROTTLE OPENING PART WAY. FRONT CARB THROUGH INTAKE MANAFOLD VAC EUALISER SUPPLYING AIR/FUEL. LOUD AIR INTAKE FRONT CARB AT IDLE. REAR CYLINDERS VERY LEAN. Throttle disk plate near closed on rear carb. has to be culprit.Please check for that vac line underneath though first. Then by book check and set your choke and throttle linkage. You may have to reset others from what you have mucked with. I go by Haynes TR manual probabley one of there last good ones and the original Leyland manual both have faults.

Please let me know. If all else fails I will go to Ray Greys little shop with hat in hand and ask for advice. Hate that because he always points out the obvious. He also builds some of the finest Jags and MG cars and classic Triumph Bikes for people.

Bill

B Brayford

Ha Bill
Thanks for your input. Yes ZS carbs. The Vacuumn line back bottom of carb to Vac retard of distributor is plugged...inactive. It is not attached to water temp. valve...do not even own on of these..must be later year. My wife gets a little upset when I spend more time with MY MSTRS than her. But then she just laughing says " I'm woking just fine".
No there is no change at clutch in/out..pops at idle and deceleration. I have good throttle response on take off and no popping at all.
Bill at this point I am tending to lean towards bad ByPassValve(s). specifically the material that allows the round disk to "slap" itself to the face on deceleration may be to stiff (not as flexible as original). When I had the racing of the engine and not able to drop idle speed ( both idle adjusting screws not even touching) it was then that I turned the BPV adjusting screw and idle went back...it actually stalled as there was no idle adjustment. So I mucked about with the BPV and was able to get the engine RPM to go up and down...BUT it was a gradual thing not a sudden jump or drop ( lack of flexability of the BPV diaphram material???). As I turned the screw I would hear more air being suck into front carb then RPM would jump up. Back it off (hissing noise goes away-less air flow) and the RPM would settle back. The back carb BPV can sit anywhere and it makes no difference as to its adjustment...maybe this is my problem. I have heard other people say that adjustment of back carb BPV makes no difference...this is weird.
The following link to the Buckeye Triumphs
http://www.buckeyetriumphs.org/index_technical.htm
has an intersting topic on our "user friendly" carbs. It talks about the BPV and adjusting both. I know I had virtually zero engine breaking when the front BPV was floating. I am thinking maybe it is time to invest in 2 BPV assemblies. The article talks about misfiring/popping with bad BPVs. The big question to me is how can I tell if the BPV is not working...more specifically if the material holding the round valve is too stiff ( not flexible enough)?
Life is never dull with a TR6.
Rick C
Rick Crawford

Hey Rick

By all my manuals 1971 Triumph carbs have no bypass adjustment whatsoever. Started in 1973. Idle trim screw only. A 1971 fitted Stromberg should not have a needle adjustment from the top of carb. My 72 does not.
Do you have a TRF parts manual. If you do try to figure out which carbs you do have. Or if by some stroke of luck the tab and # is still on top screw. I don't know about the composition of the bypass material. Your symptoms do sound a little bit like bypass apart from idle unless the bypasses are real bad. They shouhd shift at manifold vacuum low on throttle high off throttle. Hmm you may have something there. Haven't had this apart in long time. Can they be reversed? I will pull mine tomorow and take a peek. A pinhole in high vac would cause your idle problem. but why in ten minutes.

And of course again I ask what manual are you using for step by step carb adjust. Remember you are dealing with 2 carbs each able to run that engine by themselves. Sorry to harp but unless you can establish a datum line or constant. I have no idea were your at and neither do you.

Bill
B Brayford

Rick C. When I rebuilt the ZS's on my '72 last fall, the BPV's were original. The diaphram material was fabric-like that had long lost it's elasticity. Easy to see how the valve would never seat, resulting in constant lean condition. The diaphrams in renewal kits are thin rubber and solved my woes (once I got the gaskets on properly!).
Rick Orthen

Rick O
Yup...mine are original...fabric-like. As I have said, the weird thing is the back BPV has no affect on adjusting it. I do not think I am in a float state. I know the front one will "seat" but it could be slowly seating due to stiff fabric and may be "bouncing" off the seat on deceleration causing exhaust popping....that would be interesting to determine!! Intersting, the new ones are a thin rubber....thanks for this info. You say renewal kits. I do not wish to buy a carb rebuild kit ( not sure if they come in a kit anyway) so this kit is it just the 2 BPVs and required gaskets...is there a MOSS #?? Thanks Rick.
Rick C
Rick Crawford

Diaphram is Moss 365-755.
Rick Orthen

Bill
forgot to reply to you....sorry. Yes you are right that 71 did not have adjustable BPV. But then again yes they did. Ya see Rick O informed the whole world a while back that if you remove the little brass cap at the end you will discover that the adjusting screw is now accesable....SO now I know who to blame all my problems on!!..just kidin' Rick.
Bill it was 1969 that had non adjustable metering needles. Adjustable metering needles started in 1970 and included 1972. Bill I would put money on it that yours are adjustable...unless you have 1969 carbs. My tags both say C3385LH/RH which is correct for '71. The idle trim screw to me is a nice little show piece on the side of the carb and should be set to one full turn and forgotten about. The BPV really can not be reversed because of the indent and ring on the screw and spring side. One side is flat which is the seat. The brass cap will stay in place but the adjusting screw and spring ( be carefull when seperating the halves this does not go shooting across the garage) will be evident when the halves are seperated. Tap it on the work bench and the hex nut and screw will fall out of the outer piece. Obviously be carefull seperating as the diaphram is also the gasket between the 2 halves.You will now see that indeed it has a slot screw on the hidden end (behind the "removable" brass cap). My adjustments are not from a manual but posting on the WWW ( TR six pack, Buckeye). At this point I know they are ballanced and that I think I might be better off with new BPVs. Thanks Bill for your comments.
Thanks Rick O for the number. I will call my supplier and have him bring 2 to the Bronte car show. He Bill will you be there?
Rick C
Rick Crawford

Hi Rick,

Sorry to have seemed smart ass was not meant. Looking for info in archives on frame rebuilds you fellows kept popping up so obviousley you know your stuff. Consider Crow eaten but with West Nile will pass. I had some time earlier today and went to toy shop pulled them out of cupboard and apart and sure enough mine are pretty rough as well. Mine were both capped 1972 and the Leyland manual states in emissions for 72 Factory sealed to prevent tampering. I of course punched both out. Thanks Guys.

I am doing a total frame off. Sand blasting and welding in new metal as needed. Trailing arm outriggers center frame. Just bought the new cruciform plates I could not fabricate and neither could local shops. $200 with shipping and Tax. But they do say made in U.K. And then you guys point out more areas to spend money. Thanks.

Any car show is not on list for at least 2 years for my TR. What weekend is Bronte this year only went once and not as a participant.

Bill

B Brayford

Bill
Not taken that way. I kinda sounded like a SA also. So together, we will skip the crow.
As u can appreciate as soon as BL puts "tamper proof" on something one of us will figure a way to tamper with it....it is in our nature.
Bronte is next weekend on Sun,Sept. 15. ( For our southern friends Bronte is the largest British manufactured car meet of the year for Ontario...over 1000 cars. For Canada this is a big show). Ha Bill, no need to participate but do come to meet the people talkin on this BBS (from Ontario). Oh Ya, Mr. E from Montreal will likely be there also....we all know how he loves to put more miles on his 3A. There is also US entrants. When I was doing my restore, I would go to the show and peak under the hoods to see how this and that looked...the owners did not appreciate the druel though. This will be my first time participating. I am going to try to arrange to pick up 2 BPVs at the show from Fred. Maybe see you there.
Rick C
Rick Crawford


Rick,

I am pleased to report that changing out the fuel pump
Moss #377-061 has improved my rough idle at low RPM's.
My "miss" is almost completely history at low RPM's.
I think a little fine tuning on the carbs and I am
going to be on my way. If you have not tried this,
I recomend you do it.

Jeff Shirhall

Jeff
Interesting...that is 2 people this thread that have changed the fuel pump and "miss" has gone....after the new BPVs are installed and if I still have a miss will do the pump (rebuild MOSS 378-530).
Would someone give me a technical reason why a bad pump would cause a miss...is not the purpose of the float in the carb to give constant fuel level to the carbs??
Rick
Did not think this thread would end up this long...thanks for all the help guys.
Rick Crawford

Rick

According to BL book fuel pump pressure should 1.5 to 2.5 psi. Not a lot. Pumps on every second revolution. . The fuel line has a straight path to 1st carb and tees to second. I guess if pressure and volume is real low at idle the rear bowel would be starved most. I've never tested that myself but sounds plausable to me. Disable ignition take off both lines at carbs get 2 jugs. Lines into seperate jugs. Crank engine a bit. Steal your wifes measuring cup and see if you have good volume about equal in both jugs. Give measuring cup a good rinse and put back in kitchen (:

Bill
B Brayford

Hey Rick C.

How did those new BPs work out. With 27 deg. days in Oct. you can't have put Mis away.

Bill
B Brayford

Hi Bill
No way is she away! Had to put the top back down for evening driving. Hay you guys down south, yesterday record of 29*C/84*F (last was 1986 @ 26*C)...not bad for our fall and who says we do not have global warming. Anyway, yup I replaced the front one only for a trial and made no difference. The new BPV is to say the least different than original. It consists of 3 pieces instead of one. There is the valve itself with a thin rubber membrane surrounding it. The other 2 pieces are gaskets in the same shape with the center cut out for the valve. So you sandwich the membrane/valve between the 2 gaskets and you have an attempt at the original. It is over twice as thick as the original. Talk about more flexible! I found it difficult to set it. There is so much more play (valve on seat/valve off seat) that as the screw was adjusted and the valve literally "slapped" itself agains the seat ( RPMs dropped) it would also pull in the adjusting screw along with the hex screw shaft and unseat the O ring...resulting in a vacumn leak where the O ring should be! (yes the spring is in place). I have played ( another choice of word(s) should be substituded here) around with it several times and think I have got it. Still pops on deceleration and idle. At this point I think I am barking up the wrong tree and should have a closer look at the ignition side and also do a compression test.
Rick O (if you are lerking :), did you have any problems with your replacement?
Rick C
P.S. Bill do not forget Obsolete Automotive's garage sale October 26th. Good opportunity to buy at sale prices and no Tax Tax.
Rick Crawford

Rick C. Well, you did the easy front carb; when will the rear receive the new BPV? Do that before you conclude the BPV's aren't your problem. Are you positive the intake manifold is leak free? What about the vac retard port on the bottom flange of the rear carb? I know you keep your head valves in order, but a vac test may indicate an underlying problem. Replacing the BPV diaphrams on my '72 eliminated the untweakable lean (popping) condition.

I feel your pain. If it turns out to be the carbs, perhaps you should consider SU's. I'm getting ready to install a set(separate thread) to see if the rave reviews by others are true.

Rick O.
Rick Orthen

Rick O
What..do you think I would do the hard one first:) OK I will do it asap. The intake manifold has been tightened..found a couple of looseish footballs. I have done the carb cleaner thing all over that side of the engine. The vac line to the back carb is plugged at the distributor. Now, I must admit I did not sync. the carbs after replacing the front carb BPV. Will do this after the back BPV is replaced and wil go get another can of carb cleaner. Thanks Rick
Rick C
Rick Crawford

UPDATE
Put the new BPV in the back carb. No difference. Checked carb ballance ...dead on. Did not need to adjust air/fuel mixture. Turned distributor CCW ( I know ..not technical but son has the strobe light) I am sure reduced the advance. It sounded a little better but still the pop. The back carb BPV has no affect on adjustment. The front one is a different story. With the BPV on float the engine is idling high, I turn the BPV screw and no real change but if I give the screw a slight push in The screw (and the hex spring pressure adjusting thingamabob) gets sucked in as the valve seats itself and RPM drops...wierd!! If I leave it that way it seems to work but the screw is deffinitely recessed in and obviously the O ring is not seated..put my finger on the hole and does not appear that it is sucking air. Maybe I have it right and as said barking up the wrong tree.
Rick C
Rick Crawford

Rick,
33 submissions on one problem, is that a record?
All I'm going to say is ...Joe Dukovac
Christopher Trace

Joe Who ??? The only Joe Who? I know is .... well you know him too.

Don Elliott, 1958 TR3A

Does this also add another one to the new record ?

Who is this Joe Who ?
Don Elliott

christopher- I was thoinking basically the same thing when I started to read Rick's link. I hope he fixes this soon.
Just pulling your leg Rick. I wish I had a solution
Don K.
DON KELLY

This thread was discussed between 21/08/2002 and 09/10/2002

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